Miniblinds comprise a plurality of parallel slats supported in a substantially horizontal array by flexible vertically aligned ladders. Each ladder comprises a pair of elongate flexible legs and a plurality of cross rungs extending between the legs. The ladders are interlaced with the slats such that the legs are disposed on opposite sides of the array of slats and such that each slat is supported by a cross rung of each ladder. The legs of each ladder extend upwardly beyond the array slats and into a head rail.
A tilt rod is rotatably mounted in the head rail. The tilt rod has drums fixedly mounted thereon which are aligned with the ladders. The legs of each ladder extend into the head rail and are wrapped in opposite directions around the drum. Therefore, rotation of the tilt rod about its axis causes a corresponding rotation of the drum and associated longitudinal movement of the ladder legs mounted to each drum. In particular, rotation of the tilt rod causes one leg in each ladder to move upwardly while the other leg moves downwardly. This relative shifting of the legs causes an angular alignment of the cross rungs in each ladder to change, thereby causing the slats resting on the cross rungs to rotate in unison about their respective longitudinal axes.
A tilt control actuator extends from the head rail and is operatively connected to the tilt rod. The tilt control actuator rotates the tilt rod.
In theory, the slats can be tilted through an angle approaching 180.degree.. In particular, the slats may be rotated almost 90.degree. in one direction from the horizontal alignment such that a top convex surface of each slat is facing into the room in which the miniblinds are mounted. Alternatively, the miniblinds can be rotated almost 90.degree. in an opposite direction from their horizontal alignment such that a bottom concave surface of each slat is facing into the room in which the miniblinds are mounted.
One problem associated with known miniblinds is that excessive tilting of the slats could cause the miniblinds to jam. Additionally, many architectural applications of miniblinds specify controls on the tilt of miniblinds to provide a more uniform exterior appearance for the building and/or alignment of light into the building. For example, an architect may specify that miniblinds be adjustable such that only the top convex surface of each slat is viewable from the exterior of the building. Similarly, the architect may specify that the slat alignments limit vision of unsightly roadways or parking lots. Therefore, some prior art blinds include means for limiting the amount of tilt. The range of acceptable miniblind tilts may vary throughout the building.
It is known to control the amount of tilt by non-rotatably mounting a tilt control cam to a tilt rod. For instance, commonly owned U.S. Pat. No. 3,828,838 discloses tilt restriction using a generally circular tilt control cam having flat edges which abut a stop member to limit turning of the tilt control cam and the tilt rod. The flattened surface of the cam limits rotation in either direction. Varied cam configurations are provided and replacement of the cam is required to vary the amount of tilting that can take place. The tilt rod and the tilt control cam reside in a head rail. To vary the amount of tilt possible, it is necessary to replace the tilt control cam, which is only accessible from an open top of the head rail. Therefore, it may be necessary to remove the miniblind from the window to replace the tilt control cam and vary the amount of tilt.
Commonly owned U.S. Pat. No. 5,031,681 also teaches tilt restriction. Similar to U.S. Pat. No. 3,828,838, the cam is generally circular and is non-rotatably mounted to a tilt rod. A flat surface of the tilt control cam abuts a stop member. In the disclosure of U.S. Pat. No. 5,031,681, however, each tilt control cam limits rotation in a single direction, and therefore two tilt control cams are generally needed. U.S. Pat. No. 5,031,681 does not disclose alternative tilt control cam embodiments to vary the amount of tilting that can take place.
Other known tilt restriction mechanisms include a tilt control cam non-rotatably mounted to the tilt rod and having a protrusion that moves in an arcuate slot as the tilt rod is rotated. The amount of tilting that can take place is limited by permanently securing rivets within the slots to obstruct passage of the protrusion through the slot beyond the rivets. To vary the amount of tilting that can take place, the rivets must be removed and new rivets must be applied. The rivets are only accessible from an open top of the head rail. Therefore, it is likely necessary to remove the miniblind from the window to gain access to the tilt control cam.
Although the prior art tilt control cams have worked adequately, they do not allow for variation of the amount of tilting that can take place, or they require a labor-intensive procedure for altering the amount of tilting that can take place. In addition, the miniblind must be removed from the window to alter the tilt control mechanism to vary the amount of possible tilting. A skilled installer may be needed, and a variety of tools may be required. Replacement cams may be misplaced, and can be costly to purchase as needed. It could be confusing and error-prone to install miniblinds in a building such that different areas of the building require a different range of tilt. In this case, one must place the correct cam into each miniblind prior to installation. When tilt is restricted with rivets, removing rivets is complicated and could cause the plate on which the rivets are attached to break, therefore requiring replacement of the riveted plate and perhaps the entire tilt control mechanism, which would be labor-intensive and costly.
In addition to installation problems, it has been noted in the industry that tolerance cannot be held to a precise, finite measurement for the size, shape and placement of many of the elements of the miniblind, including the tilt control cam, the stop member which the tilt control cam abuts, the retainer, the tilt rod, the head rail, the ladder headloop, the tilt actuator and the drum. These components, when measured within their respective tolerance limits, can change the open and close positions significantly, sometimes more than 20.degree.. With each combination of the above-listed elements, a different angle is obtained, and the product may not meet the customer's expectations.